The present invention relates to functionalized silicas, a process for their preparation and their use.
It is known to react silicon dioxide obtained by flame hydrolysis and with a surface area of 40 to 200 m2/g with 3-methacryloxypropyltrimethoxysilane. The resulting silicon dioxide is then coated with a further shell of (meth)acrylate polymers and subsequently employed in dental compositions (EP 0 142 784 A1).
The present invention provides functionalized silicas, characterized by functional groups fixed on the surface, the groups being 3-methacryloxypropylsilyl and/or glycidyloxypropylsilyl.
The present invention also provides a process for the preparation of the functionalized silicas, which is characterized in that a silica is sprayed optionally first with water or dilute acid and then with a surface modification reagent or a mixture of several surface modification reagents in a suitable mixing vessel, with intensive mixing, the components are optionally re-mixed for 15 to 30 minutes and heat-treated at a temperature of 100 to 400xc2x0 C. over a period of 1 to 6 h.
A silica prepared pyrogenically by the route of flame hydrolysis of SiCl4 can preferably be employed as the silica. Such pyrogenic silicas are known from Ullmanns Enzyklopxc3xa4die der technischen Chemie [Ullmanns Encyclopaedia of Industrial Chemistry], 4th edition, volume 21, page 464 (1982).
In a preferred embodiment of the invention, a pyrogenic silica with a surface area of approx. 200 m2/g can be employed (Aerosil(copyright) 200).
Monomeric substances, such as 3-methacryloxypropyltrialkoxysilane and/or glycidyloxypropyltrialkoxysilane, wherein alkoxy can be methoxy, ethoxy and/or propoxy, can be employed as the surface modification reagent.
The amount of silane can be metered with respect to the silica such that no or only a small excess results. The excess silane can optionally be removed during the heat treatment.
The silica according to the invention can be employed in solvent-containing coatings, for example 2-component polyurethane coatings.